NAME
Pegex - Pegex Parser Generator
SYNOPSIS
use Pegex;
my $data = pegex($grammar)->parse($input);
or with regular expression sugar:
use Pegex::Regex;
$input =~ qr{$grammar}x;
my $data = \%/;
or more explicitly:
use Pegex::Grammar;
use Pegex::Compiler;
my $pegex_grammar = Pegex::Grammar->new(
tree => Pegex::Compiler->compile($grammar)->tree,
);
my $data = $pegex_grammar->parse($input);
or customized explicitly:
package MyGrammar;
use Mo;
extends 'Pegex::Grammar';
has text => default => sub {
"your grammar definition text goes here";
};
has receiver => default => sub{"MyReceiver"};
package MyReceiver;
use base 'Pegex::Receiver';
got_some_rule { ... }
got_other_rule { ... }
package main;
use MyGrammar;
my $grammar = MyGrammar->new();
$grammar->parse($input);
my $data = $receiver->data;
DESCRIPTION
Pegex is a Acmeist parser framework. It allows you to easily create
parsers that will work equivalently in lots of programming langugages!
Pegex gets it name by combining Parsing Expression Grammars (PEG), with
Regular Expessions (regex). That's actually what Pegex does.
PEG is the cool new way to elegantly specify recursive descent grammars.
The Perl 6 language is defined in terms of a self modifying PEG language
called Perl 6 Rules. Regular expressions are familar to programmers of
most modern programming languages. Pegex defines a simple PEG syntax,
where all the terminals are regular expressions. This means that Pegex
can be quite fast and powerful.
Pegex attempts to be the simplest way to define new (or old) Domain
Specific Languages (DSLs) that need to be used in several programming
languages and environments.
Pegex MODULE USAGE
The "Pegex.pm" module itself is just a trivial way to use the Pegex
framework. It is only intended for the simplest of uses.
This module exports a single function, "pegex", which takes a single
value, a Pegex grammar. The grammar value may be specified as a string,
a file name, or a file handle. The "pegex" function returns a
Pegex::Grammar object, on which you would typically call the "parse()"
method, which (on success) will return a data structure of the parsed
data.
PEGEX OVERVIEW
In the diagram below, there is a simple language called Foo. The diagram
shows how Pegex can take a text grammar defining Foo and generate a
parser that can parse Foo sources into data (abstract syntax trees).
Parsing a language called "Foo"
with the Pegex toolset.
.-----------------------.
.--------------------. | Pegex::Compiler |
| Foo Language | |-----------------------| Serialize
|--------------------|----->| Pegex::Grammar::Pegex |---------.
| Pegex grammar text | | Pegex::Receiver | |
'--------------------' '-----------------------' v
...................... | .------.
| | | compile() | YAML |
|foo:: | v '------'
|verb: /Hello/ | .--------------------. .------.
|noun: /world/ | | Foo grammar tree | | JSON |
| | '--------------------' '------'
...................... | .------.
| | Perl |
v '------'
.---------------------. .--------.
| Pegex::Grammar::Foo | | Python |
|---------------------| '--------'
| Pegex::Parser | .-----.
| Pegex::AST::Foo | | etc |
.-----------------. '---------------------' '-----'
| Foo Language | |
|-----------------|------------------->| parse()
| Foo source text | v
'-----------------' .----------------------.
................... | Parsed Foo Data Tree |
|Hello world | '----------------------'
................... ........................
|- verb: Hello |
|- noun: world |
........................
FYI
Pegex is self-hosting. This means that the Pegex grammar language syntax
is defined by a Pegex grammar! This is important because (just like any
Pegex based language) it makes it easier to port to new programming
languages. You can find the Pegex grammar for Pegex grammars here:
.
Pegex was originally inspired by Perl 6 Rules. It also takes ideas from
Damian Conway's Perl 5 module, Regexp::Grammars. Pegex tries to take the
best ideas from these great works, and make them work in as many
languages as possible. That's Acmeism.
SELF COMPILATION TRICKS
You can have some fun using Pegex to compile itself. First get the Pegex
grammar repo:
git clone git://github.com/ingydotnet/pegex-pgx.git
cd pegex-pgx
Then parse and dump the Pegex grammar with Pegex:
perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx")->parse("pegex.pgx")'
For a different view of the data tree, try:
perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx", {wrap => 0})->parse("pegex.pgx")'
Finally to emulate the Pegex compiler do this:
perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx", {receiver => "Pegex::Pegex::AST"})->parse("pegex.pgx")'
This specifies a "receiving" class that can shape the results into
something useful. Indeed, this is the exact guts of
Pegex::Grammar::Pegex.
A REAL WORLD EXAMPLE
TestML is a new Acmeist unit test language. It is perfect for software
that needs to run equivalently in more than one language. In fact, Pegex
itself is tested with TestML!!
TestML has a language specification grammar:
http://www.testml.org/specification/language/
The Perl6 implementation of TestML uses this grammar in:
https://github.com/ingydotnet/testml-pm6/blob/master/lib/TestML/Parser/G
rammar.pm
All other implementations of TestML use this Pegex grammar:
https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx
In Perl 5, Pegex::Compiler is used to compile the grammar into this
simple data structure (shown in YAML):
https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx.yaml
The grammar can also be precompiled to JSON:
https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx.json
Pegex::Compiler further compiles this into a Perl 5 only grammar tree,
which becomes this module:
https://github.com/ingydotnet/testml-pm/blob/master/lib/TestML/Grammar.p
m
TestML::Parser::Grammar is a subclass of Pegex::Grammar. It can be used
to parse TestML files. TestML::Parser calls the "parse()" method of the
grammar with a TestML::AST object that receives callbacks when various
rules match, and uses the information to build a TestML::Document
object.
Thus TestML is an Acmeist language written in Pegex. It can be easily
ported to every language where Pegex exists. In fact, it must be ported
to those languages in order to test the new Pegex implementation!
SEE ALSO
* Pegex::Manual
* Pegex::Grammar
* Pegex::Regex
*
* irc.freenode.net#pegex
AUTHOR
Ingy döt Net
COPYRIGHT AND LICENSE
Copyright (c) 2010, 2011. Ingy döt Net.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
See http://www.perl.com/perl/misc/Artistic.html